Russ,
All my Flatheads thru the years had a cruising sweet spot...
the motor sort of told me where it was happy. Since blowning my
Columbia up I'm now temporarily using a straight 3:78 . With 276
inches 55 is where it seems happy in 3rd. It'll do 55 in 2nd no sweat
but so what. The idea of leaving a bit early makes sense to moi !
Charlie ny